The accuracy of a sensor arrangement is determined by the relationship between its electronic components and the packaging (housing) that locates the active elements of the sensor in space. Under normal circumstances any errors in the packaging of the elements of the assembly will result in an error in the final position of the active sensor elements with respect to the article/object which is to be scanned and/or otherwise subjected to inspection.
In the case a sensor arrangement includes a lens array which is designed to focus an image on a photo responsive device, such as a charge couple device (CCD) or the like type of opto-electric transducer, any error in the setting of the lens array with respect to the transducer, or vice versa, is apt to cause a blurring, distortion or the like, of the image/data which is developed. The problem is further compounded in the instance that a mirror or prism is used to direct the image into the lens array in that any deviations in the angle and disposition of the mirror with respect to the lens array is, of course, apt to induce accuracy problems.
In devices such as image readers and scanners which are used to read information printed on the surface of an article such as a sheet of paper, envelope, etc., accuracy is paramount and any constructional/assembly errors which reduce this accuracy are apt to render the device partially or totally inoperative for its intended purpose.
The active elements, such as the lens array and the opto-electric transducer may be incorporated into a sub-housing or casing which is adapted to be mounted in the interior of a larger device, such as an optical scanner or the like. However, if these active elements are not precisely located within the sub-housing in a manner wherein the combined effect of the various deviations, which occur as a result of manufacturing and/or assembly, does not fall in an acceptable range, then the whole unit will produce unacceptable results. This, of course, results in the rejection of the unit.
In order to reduce/eliminate the number of units which are rejected for the above mentioned reason, it is necessary to tighten the manufacturing tolerances on each of the individual components as well as those pertaining to their assembly, so as to reduce unnecessary expense of rejecting a fully assembled unit. This of course raises the manufacturing costs and reduces productivity.
Circumnavigating these problems is difficult in as much as there is a tendency to use the unit housing as a reference and attempt to locate all of the elements which are disposed therein, in a very precise spatial relationship with respect to the housing and thus produce a unit which can be mounted in a larger device using preformed location features.
U.S. Pat. No. 5,565,674 discloses an example of the above mentioned type of arrangement. As shown in FIG. 1, this arrangement includes an optical package 10 having a molded, optically clear body 12 surrounding the central portion of a wing-shaped support 14. This support has two wing-shaped portions 16A and 16B with mounting holes 18A and 18B extending therethrough for receiving mounting screws and permitting the optical package 10 to be mounted to the head of an optical CD read/write system. With this arrangement it is clear that if the active elements are, for any reason, not located within a predetermined tolerance with respect to the mounting holes 18A, 18B then the package is apt not to come up to specification and to be subject to rejection.